Italy's highest appeals court has criticised "glaring errors" in the investigation into the 2007 murder of British student Meredith Kercher.
The court acquitted Amanda Knox and her ex-boyfriend Raffaele Sollecito of the murder in March.
It said there was an "absolute lack of biological traces" of either defendant in the room where Ms Kercher was killed and on her body.
Ms Kercher, 21, was stabbed to death in a Perugia flat she shared with Ms Knox.
The Court of Cassation, which exonerated the pair, published its reasoning on Monday, as it is required to do under Italian law.
It issued a damning assessment of the quality of the prosecution case, saying its high profile nature had an effect on investigators.
"The international spotlight on the case in fact resulted in the investigation undergoing a sudden acceleration,'' the court said.
Several mistakes in the investigation were outlined by the court in its reasoning, including the fact that investigators burned Ms Knox's and Ms Kercher's computers, which could have yielded new information.
The court also wrote that the Florence appeals court which convicted the pair last year ignored expert testimony that "clearly demonstrated possible contamination'' of evidence and misinterpreted findings about the knife allegedly used to slit Kercher's throat, in what prosecutors had described as a sexual assault, AP reports.
"The kitchen knife, found in Sollecito's house and the supposed crime weapon, was kept in an ordinary cardboard box,'' the judges noted, adding that no traces of blood were found on it.
The judges said that one of Ms Kercher's bra clasps, which prosecutors argued carried a trace of Mr Sollecito's DNA, was left on the floor of the murder scene for 46 days, and then "was passed from hand to hand of the workers, who, furthermore, were wearing dirty latex gloves".
Another man, Rudy Hermann Guede, born in Ivory Coast, was convicted of murder in a separate trial and is serving a 16-year sentence.
The court's ruling against Guede stated that he did not act alone, but the acquittals of Ms Knox and Mr Sollecito mean that no-one now stands convicted of acting with Guede to kill Ms Kercher.
- 1 November 2007: Kercher is killed at her apartment in Perugia. Police find her a day later.
- 6 November 2007: Kercher's American housemate Knox is arrested, along with Sollecito and Congolese national Patrick Diya Lumumba.
- 20 November 2007: Rudy Guede detained in Germany and extradited to Italy. Mr Lumumba released without charge
- 28 October 2008: Guede sentenced to 16 years. A judge rules Sollecito and Knox will face a murder trial
- 4 December 2009: Knox and Sollecito found guilty of murder and sexual violence, and jailed for 26 and 25 years
- 3 October 2011: Knox and Sollecito acquitted
- 31 January 2014: Convictions re-instated
- 28 March 2015: Court of Cassation acquits Knox and Sollecito in final verdict